U.S. patent number 3,850,477 [Application Number 05/375,280] was granted by the patent office on 1974-11-26 for chemical comminution and mining of coal.
This patent grant is currently assigned to Syracuse University Research Corporation. Invention is credited to Robert G. Aldrich, Douglas V. Keller, Jr., Richard G. Sawyer.
United States Patent |
3,850,477 |
Aldrich , et al. |
November 26, 1974 |
CHEMICAL COMMINUTION AND MINING OF COAL
Abstract
Coal, whether in a sub-surface stratum or in large lumps as
mined by standard means is reduced to fragments by treatment with
compounds which weaken interlayer forces at natural interfaces
present in the coal. When coal below the earth's surface is treated
with such compounds, the fragments can be suspended in inert gas
moving at a sufficiently rapid rate and carried to the surface
where the comminuted coal can be collected.
Inventors: |
Aldrich; Robert G. (Manlius,
NY), Keller, Jr.; Douglas V. (Lafayette, NY), Sawyer;
Richard G. (Syracuse, NY) |
Assignee: |
Syracuse University Research
Corporation (Syracuse, NY)
|
Family
ID: |
26925877 |
Appl.
No.: |
05/375,280 |
Filed: |
June 29, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
232324 |
Feb 18, 1972 |
3815826 |
|
|
|
Current U.S.
Class: |
299/5; 208/400;
166/307; 299/18; 406/47 |
Current CPC
Class: |
E21B
43/29 (20130101); C10L 9/00 (20130101); E21C
37/00 (20130101); E21B 43/28 (20130101) |
Current International
Class: |
C10L
9/00 (20060101); E21C 37/00 (20060101); E21B
43/29 (20060101); E21B 43/28 (20060101); E21B
43/00 (20060101); E21c 041/04 () |
Field of
Search: |
;299/4,5,17 ;175/64,12
;44/51 ;208/8 ;302/66,22,40,45,46 ;166/271,307,308 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Purser; Ernest R.
Attorney, Agent or Firm: Blum, Moskovitz, Friedman &
Kaplan
Parent Case Text
This is a division, of application Ser. No. 232,324, filed Feb. 18,
1972 and now U.S. Pat. No. 3,815,826.
Claims
What is claimed is:
1. A method of mining sub-surface coal comprising the steps of
forming at least one opening into a sub-surface stratum of solid
coal, injecting into said sub-surface stratum an effective amount
of a compound selected from the group consisting of substantially
anhydrous liquid ammonia, anhydrous gaseous ammonia, anhydrous
methanol, anhydrous methanol containing about one-fourth mole of
sodium hydroxide per liter, anhydrous ethanol, anhydrous ethanol
containing about one-fourth mole of sodium hydroxide per liter,
anhydrous isopropanol, anhydrous isopropanol containing about
one-fourth mole of sodium hydroxide per liter, glacial acetic acid,
70 percent ethylamine, 40 percent methylamine, pure acetone, 3
percent hydrogen peroxide and a mixture consisting of 150 ml of
anhydrous methanol, 50 ml of distilled water and one-fourth mole of
sodium hydroxide, said compounds being capable of reducing
interlayer forces at natural interfaces present in said coal,
injecting an inert gas into the region of said sub-surface stratum
of coal treated with said compound at a rate high enough to form a
suspension of coal particles in said inert gas, and leading said
suspension of comminuted coal in inert gas to the surface for
collection of said comminuted coal.
2. The method of claim 1, wherein said comminuting compound and
said inert gas are forced through one of two pipes leading through
said opening from the surface to said stratum of coal and said
suspension of comminuted coal in inert gas is led to the surface
through the other of said pipes.
3. The method as defined in claim 1, wherein said pipes are
essentially concentric.
4. The method as defined in claim 1, wherein said comminuting agent
is introduced through said opening into said stratum of coal,
allowed to remain in contact with said coal for a period sufficient
for comminution of said coal, after which said inert gas is
introduced to form said suspension and carry said suspension
through said opening to the surface.
5. The method as defined in claim 1 further comprising the step of
fragmenting said coal in said stratum with a boring-tool.
6. A method of mining sub-surface coal as defined 1n claim 1,
wherein said compound is one of the following solutions, the two
members of each solution being present in roughly equal volumes, 40
percent methylamine with anhydrous methanol, 70 percent ethylamine
with anhydrous ethanol, anhydrous methanol with acetone, anhydrous
ethanol with acetone, anhydrous isopropanol with acetone, glacial
acetic acid with acetone.
Description
BACKGROUND OF THE INVENTION
According to usual coal-mining procedures, sub-surface coal is
broken into pieces of manageable size by the use of explosives,
picks or other mechanical means, and finally brought to the surface
mostly in the form of large lumps which are then broken down by
mechanical procedures such as crushing, milling, grinding,
pulverizing, etc. The degree of reduction in size is suited to the
application for which the coal is to be used.
Methods have been disclosed wherein the addition of inorganic or
organic salts and weak aqueous solutions have supressed the
formations of fragments in the airborne size range during
conventional coal cutting, although no particular advantage was
cited in the size reduction processes (Poelnev, A.P., et al.,
"Control of Coal Dust in Mines," Akad. Nauk SSR Sb. Statu 7 (1967),
72.)
The usual methods for the breakage of coal which is found in the
natural state as massive solid beds include the use of drilling,
cutting or explosive mining techniques as aforenoted. All of these
are normally used in conjunction with each other and require an
excessive energy expenditure including man power. Since numerous
industrial processes which consume coal use the extracted product
in particulate form, e.g. one-half inch size or less, further size
reduction operations are required. Each of these subsequent
processes employed for further particle size reduction requires
large additional expenditures of energy and produces excessive
volumes of coal dust, hazardous due to its explosive nature and the
effect on the health of workers carrying out the operations.
SUMMARY OF THE INVENTION
The treatment of coal with compounds disclosed herein results in
fracture of the coal by weakening of the interlayer forces at
natural interfaces present in the coal. The weakening of the forces
is sufficiently great so that in some cases, the coal breaks into
particles small enough to be airborne without the application of
further force. Other compounds disclosed herein, when applied to
coal, weaken the interlayer forces sufficiently so that only
minimal energy is required to fragment the coal.
The chemical comminution of coal can be used for mining coal from
sub-surface strata by injecting any of said compounds into a
sub-surface stratum, following this with the injection of an inert
gas at a rate high enough to form a suspension, and carrying the
suspension back to the surface where the comminuted coal is
separated from the carrier gas.
Accordingly, an object of the present invention is to provide a low
energy consumption method for the fragmentation of raw coal.
Another object of this invention is to provide a low energy
consumption method for the fragmentation of raw coal in natural
beds or seams.
A further object of the present invention is to provide a low
energy consumption method for the fragmentation of coal during the
preparation of coal subsequent to its retriveal from a mine.
Yet another object of this invention is to provide a method for the
fragmentation of coal which is free of airborne dust
production.
Yet a further object of this invention is to provide a means for
particle size reduction of coal without affecting the particle size
of rock or mineral impurities.
A significant object of the present invention is to provide an
improved means for fragmentation of coal without detriment to the
calorific value of the coal.
A further object of the present invention is to provide an improved
basis for rock and mineral impurity separation from coal.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
The invention accordingly comprises the several steps and the
relation of one or more of such steps with respect to each of the
others thereof, which will be exemplified in the method hereinafter
disclosed, and the scope of the invention will be indicated in the
claims.
BRIEF DESCRIPTION OF THE DRAWING
For a fuller understanding of the invention, reference is had to
the following description taken in connection with the accompanying
drawing, in which:
The single FIGURE shows schematically the fragmentation and mining
of coal in accordance with the method of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A number of materials have been found which when brought in contact
with coal weaken interlayer forces to a useful extent. In view of
the fact that these compounds affect surface forces, they will be
referred to as surface active agents or wetting agents despite the
fact that these compounds are not normally so regarded.
It is known that aqueous solutions of ammonia and a number of other
inorganic compounds tend over a long period of time to cause
interlayer weaknesses in the natural interfaces of coal; however,
such compounds have not been effective to accomplish purposes of
the invention. The ability of small molecules to diffuse through
the internal surface structure of coal appears to be essential to
accomplish the purposes set forth. For example, anhydrous ammonia
in the liquid or gaseous state in contact with massive coal
immediately impregnates the coal structure causing a reduction in
internal boundary strength to near zero. The massive coal system
after impregnation has almost no resistance to a crushing force;
some coals virtually collapse under their own weight to a finely
divided coal product when treated with anhydrous ammonia or other
compounds to be named below.
A preferred method of particle size reduction would initiate in the
natural coal bed itself wherein the finely divided coal is removed
as the product of the combined action of, for example,
substantially anhydrous liquid (or gaseous) ammonia under pressure
and mechanical devices which essentially form a boring tool. The
boring tool is first used as a means of reaching a sub-surface coal
seam and providing a passage through which one or more pipes can be
inserted into the seam. The pipes essentially seal the passage, and
the pipes can be arranged, preferably essentially concentrically,
so that wetting agent and inert carrier gas can be brought to the
seam, and a fluidized suspension of comminuted coal can be brought
to the surface where finely divided contaminants can be separated
from the suspension. The ammonia can be recovered by a suitable
process for recycling. The coal particles can then be classified
for further size reduction in an ammonia atmosphere, for further
contaminant isolation or for direct sale.
The single FIGURE shows schematically how such a process is carried
out. Wetting agent, stored in tank 1 is supplied to pipe 2 and
transported therethrough to coal seam 3 lying below the surface of
the earth 4. An inert gas stored in tank 6 is likewise transported
through pipe 2 to coal seam 3. The rate of supply of inert gas is
such that coal fragments produced by contact of the wetting agent
with the coal seam are fluidized and carried upward through pipe 7.
From pipe 7 the fluidized product is carried to separator 8 which
screens the coal fragments from rock and other impurity objects
which are of larger size. The fragmented coal is transferred to
coal storage bin 9. Such wetting agent as is recovered in separator
8 is transferred back to tank 1. Similarly, the inert gas used for
fluidizing the coal fragments is returned to inert gas storage tank
6. The various pumps, valves, etc. necessary for the operation are
not shown since the provision of such accessories would be within
the skill of one familar with the art. Furthermore, although pipes
2 and 7 are shown as being concentric this is merely a matter of
convenience since the drilling of only one hole is required with
such an arrangement. Also, three concentric tubes could as
conveniently be used, one to carry the wetting agent, a second to
carry the inert gas, and the third to lead the fluidized coal
fragments to the surface.
Treatment of coal chunks with the wetting agents of the present
invention is also useful where the chunk coal is obtained by strip
mining operation or by standard techniques. In such cases, the
fluidizing technique is not needed.
Essential to the process is the exposure of massive or chunk coal
to a surface active agent such as liquid or gaseous ammonia,
methanol or other organic compounds of molecular weight less than
100, including some as solvents with the addition of inorganic
compounds which effect a substantial drop in internal boundary
strength. No precise time, temperature or pressure can be specified
for the impregnation step as it will naturally depend on the
morphology and chemistry of the coal and the ability of the agent
to diffuse through all of the interfaces. Time, temperature and
pressure control the rate of diffusion.
The postulated mechanism for the decrease in boundary strength due
to the effects of the surface active agents is as follows: the low
molecular weight ammonia, for example, penetrates the massive coal
structure by rapid diffusion and capillary along the natural
bedding planes and other structural defects of the coal. The strong
hydrogen bonding ammonia is adsorbed on each of the two surfaces
constituting the boundary, renders the natural atomic bonding
system of the interface inactive and substitutes a boundary surface
which has little attractive force for its counterpart surface. The
consequence is that all boundaries which were exposed have
essentially no resistance to applied forces. Since only natural
boundaries or internal surfaces are attaacked, i.e., homogeneous
volumes do not appear to be affected, and since these surfaces are
the most likely for the precipitation of sulfur bearing deposits,
fracture along these planes will expose the non-coal constituents
and facilitate the removal of such impurities.
The generation of fine particles with a hydrogen bonded film of
ammonia or other surface active agent facilitates transport. The
presence of the adsorbed surface active agent film is not
detrimental to the calorific value of the coal and does not induce
deleterious side reactions which could present a health hazard or
interfere with industrial processing.
The process of the invention is further illustrated by the
following examples:
Samples of Illiniois No. 6, Lower Cherokee and Pittsburgh coals
approximately 5 inches in length, 5 inches in width and 5 inches in
thickness were cut from larger pieces and placed in separate glass
containers at room temperature. A mixed stream of gaseous and
liquid anhydrous ammonia was directed at each sample individually
for a period of approximately three minutes. During this period
continuous visual observations were made as to the extent of
spontaneous breakage in each sample.
Within 1-2 minutes after the start of sraying both the Lower
Cherokee and Illinois No. 6 coals began crumbling without the
application of any externally applied force. During a 30 minute
standing period coal particles spontaneously fragmented were
typically in the size range 100 mesh X O. In the case of Pittsburgh
coal an approximate time of 5 minutes elapsed before significant
breakage occurred with the fragmented particles typically in the
size range 10 mesh X O. It was observed in all tests that non-coal
contaminants, e.g. pyrite, calcite, shale, rock, were not
significantly affected by exposure to this environment. Pieces of
these materials up to three-fourth inch in size were found after
exposure. Microscopic examination of the fragmented coal particles
subsequent to breakage indicated that the particles tended to have
irregular shapes with sharply defined edges such as would be
expected as a consequence of brittle fracture. The absence of any
rounded or smoothed particle shapes further illustrated that the
application of anhydrous ammonia had not signifcantly interacted to
dissolve or otherwise modify the bulk structure of the coal.
Chemical interactions are postulated to have occurred within
adjoining surficial layers of macroscopic and microscoic internal
boundaries within the coal.
In order to verify that no portion of the observed effect was
attributable to the low temperatures of the liquid-gas ammonia
stream additional experiments were performed wherein samples of
Illinois No. 6 and Pittsburgh coals were immersed in tap water at
room temperature for one hour, cooled in air at an approximate rate
of 50.degree.F/hour to 0.degree.F, and thawed at room temperature
in tap water. No effects were observed to occur during or as a
consequence of these processes. Similarly a sample of Lower
Cherokee coal was chilled by immersion in a liquid-gas stream of
nitrogen for approximately 5 minutes and thawed in air. Microscopic
examination indicated that coal breakage had not been effected by
the freezing process.
Samples of Illinois No. 6, Lower Cherokee and Pittsburgh coals
approximately 3 inches in length, 4 inches in width and 3 inches in
thickness were placed separately in glass containers filled with a
mixture of 150 ml anhydrous methanol, 50 ml distilled water and
one-fourth mole sodium hydroxide. To ensure a minimum of moisture
pickup from the air the sample containers were placed separately in
desiccators with calcium chloride added. The samples were allowed
to stand for several hours; at selected regular intervals each was
examined to determine breakage effects induced by the methanol.
After 1 hour exposure light tapping of the coal resulted in
significant breakage and after 3 hours spontaneous fragmentation
had progressed sufficiently to reduce the coals to the 10 mesh X O
size range.
Table 1 shows compounds which have been tested and found effective
in the comminution of lump coal.
TABLE 1
WETTING AGENTS
Substantially anhydrous methanol
Substantially anhydrous methanol plus one-fourth mol NaOH/liter
Substantially anhydrous ethanol
Substantially anhydrous ethanol plus one-fourth mol NaOH/liter
Substantially anhydrous isopropanol
Substantially anhydrous isopropanol plus one-fourth mol
NaOH/liter
Glacial acetic acid
70 percent Ethylamine
40 percent Methylamne
Acetone
3 percent Hydrogen peroxide
It will be noted that all of the compounds listed are below 100 in
molecular weight.
A number of mixtures of these wetting agents have also been found
to be effective in fragmentation of lump coal. Such mixtures are
listed in Table 2. In each of the binary solutions listed, the
components are present in equal volumes.
TABLE 2
WETTING AGENTS
40 percent methylamine/anhydrous methanol
70 percent ethylamine/anhydrous ethanol
anhydrous methanol/acetone
anhydrous ethanol/acetone
anhydrous isopropanol/acetone
glacial acetic acid/acetone
It has been observed that total immersion in the liquid phase of
whatever surface active agent is used is not a necessary condition,
although the rate of reaction may be greater if the coal is totally
immersed. The quantity of reagent required for comminuting a unit
weight of coal is directly dependent upon the particular reagent
used, the final physical and chemical specifications of the coal
product and the nature of the specific mining or processing
techniques employed.
Results obtained thus far indicate that about 100 pounds of reagent
are required per ton of coal. The net loss of reagent, that is the
fraction of reagent not recoverable, has been found to be about 4
pounds per ton of coal, so that the efficiency of agent recovery is
about 96 percent.
Tests have shown that the concentration of alkali in alcohol is not
critical, and have also shown that the ratio of reagents in
mixtures need not be 1 to 1 by volume. For instance, a solution
consisting of 40 parts of methanol and 60 parts of methylamine has
been found to be effective. This is evident from the fact that a
mixture consisting of 150 ml of anhydrous methanol, 50 ml of
distilled water and one-fourth mole of sodium hydroxide has been
found to be effective.
Although it appears that the effectiveness of the various compounds
and mixtures listed above is due to their low molecular weight, and
to their ability to form hydrogen bonds to carbon at interfaces,
the invention is not to be deemed dependent on any particular
theory of mode of operation or limited to the specific methods
illustrated.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in carrying out the
above method without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description shall be interpreted as illustrative and not in a
limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described, and all statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
* * * * *